Cone impedance question


I own  pair of nice 2.5 way, 4 ohm floorstanders and recently destroyed the 2 woofers on one of them. The story would be too long so I'll spare you.

Since no replacement parts are available (per the US Distributor) I had the bright idea of acquiring a used pair of the matching 2 way bookshelvers which also feature the "same" 5 1/4" cone, with the intent of canibalizing those cones to fit in my broken floorstander. I found out the "same" is not quite.

The cones are almost identical physically, those removed from the bookshelves have a cover over the magnets that I assume are a magnetic shield but the fundamental difference is impedance. The broken ones are labeled as 7.2 ohm, while the replacements are 3.6 ohm.

While installing I have balanced the cones so each floorstander has one 7.2 ohm and one 3.6 ohm cone, rather than one speaker (original) with two 7.2 ohm and the repaired with two 3.6 ohm cones.

When listening I am not noticing any differences, but then I haven't listened to these speakers for over a year.

I am looking for comments on potential implication. For example

  • I have changed the total impedance of the speakers. Am I now at less than 4 ohm?
  • Any one know of any obvious sound implications? I would assume the voicing of the cones would be the same even though the impedance difference.
Any comments would be greatly appreciated. Thanks,

Javier


Ag insider logo xs@2xvjsanaiz
Two 7.2 ohm in parallel is the same impedance as one 3.6 ohm woofer.

The crossover is designed to work with a 3.6 ohm load on the woofer.

By combining a 3.6 and a 7.2 you have a woofer load of  2.4 ohm which is too low.
Thanks for the explanation, so I may overload the power amp?

Can it also damage the crossover?
Impedance is a parameter necessary to design the crossover.

The crossover will not “work” with the new drivers.
I'm going to give you advice you will not take. This happens at work often too.

The hardest thing newbies do is try to replace a woofer for an existing speaker, while keeping everything else the same. It is nearly impossible to do well. Of course, if you find identical parts, that's not the issue.

You are far better off spending more time looking for identical replacements. Either by hitting up the DIY boards where someone may recognize the driver and model, or as you alluded, going to e-bay and looking for replacements or other speakers to cannibalize.

It is far far easier to build a new speaker from a kit, or even learning to design a 2-way/3-way speaker from scratch, than it is to take any existing design and find a replacement woofer for it without also knowing how to change the crossover.

Best,

E
http://businessfinder.pennlive.com/7275198/TriState-Loudspeaker-ReConing-Aliquippa-PA
Tri State Loudspeaker outside of Pittsburgh can rebuild virtually any speaker.  They are not fast and usually inexpensive.  They get shipments from all over the world, including NASA.  Kind of crazy work they do for a tiny little shop run out of a home.  I've seen them rebuild mega bucks subwoofer columns for live venues and then turn around and work on vintage AR speakers.